Assembly automation is a set of lines and special-purpose machines, built to one customer's order, which assemble a product, dispense adhesive and test it with hardly a hand touching it. Each line is designed for one product, so the makers are engineering firms that build a new line for each customer.
A line is a series of stations. At each station, one task is done. A part is placed, a screw is tightened, a bead of glue is laid, or a test is run. The product moves from station to station on a conveyor. The time that each station takes is the cycle time, and the slowest station decides how fast the whole line runs.
Take, for example, a plant in Noida that makes casings for electricity meters. The line has six stations. The cycle time is 4 seconds, so the line makes 900 casings an hour. A robot places the circuit board. A dispenser lays a bead of glue around the edge. A press closes the casing. A camera checks the glue line, and a printer marks a serial number. A PLC controls the stations and keeps their timing. Each casing's result goes to the MES.
The air that moves the parts comes from compressors and pneumatics. The serial number comes from an inkjet coding printer.
The slowest station decides the speed of the whole line. If the glue station needs 5 seconds, not 4, the line makes only 720 casings an hour, however fast the other stations are. So the engineers who design the line spend much effort on balancing the stations, so that no single station is slower than the rest. A line also stops when one station fails, so each station has sensors that report why it stopped.
A customer pays for a line as a project, with a fixed delivery date and a guaranteed output per hour. Because every line is a one-off project, the maker's engineers stay with it for years, to fix and to change it. To teach this skill, colleges use a small working line, the learning factory.